Electrode holder for electric arc furnace and make the same

ABSTRACT

An electrode holder having a powder metallurgical liner suitable for an application of an electric arc furnace using a high electric power as well as an ultra high electric power. The liner is fabricated from a porous powder metallurgical plate itself or the plates sintered on one side or both sides of a metal plate comprising at least one of metal powder selected from the group consisting of copper, iron and aluminum powders with or without graphite powder, an additional metal powder and if necessary, together with carbon fiber or graphite fiber.

United States Patent 1 Yoshimura et al.

[451 Feb. 20, 1973 ELECTRODE HOLDER FOR ELECTRIC .ARC FURNACE AND MAKE THE SAME Inventors: Tsuneo Yoshlmura; Kunlo Suzuki, Tokyo; Gohel Shlkano, Chigasaki, all of Japan Assignees: Mitsubishi Seiko Kabushiki Kaisha; Toyo Carbon Kabushiki Kaisha, Tokyo Filed: Nov. 5, 1970 App]. No.: 87,086

Foreign Application Priority Data Nov. 12, 1969 Japan ..44/90676 Oct. 13, 1970 Japan ..45/89329 Oct, 13, 1970 Japan ..45/89330 US. Cl ..29/l82.3, 13/16, 75/208 R Int. Cl. ..H05b 7/12 Field of Search ..29/l82.2, 182.3, 182.5, 182; 75/200, 201, 208, 214; 13/15, 16

References Cited UNITED STATES PATENTS 6/1972 Smith ..13/16 3,535,093 10/1970 Sara ..29/l82.5 3,307,924 3/1967 Michael ..29/182.5

FOREIGN PATENTS OR APPLICATIONS 1,185,414 3/1970 Great Britain ..13/16 238,004 7/1959 Australia ..75/201 8,841 5/1966 Japan ..75/201 Primary Examiner-Benjamin R. Padgett Assistant Examiner-B. I-l. I-lunt Attorney-Bosworth, Sessions, l-lerrstrom & Cain [57] ABSTRACT An electrode holder having a powder metallurgical liner suitable for an application of an electric arc furnace using a high electric power as well as an ultra high electric power. The liner is fabricated from a porous powder metallurgical plate itself or the plates sintered on one side or both sides of a .metal plate comprising at least one of metal powder selected from the group consisting of copper, iron and aluminum powders with or without graphite powder, an additional metal powder and if necessary, together with carbon fiber or graphite fiber.

6 Clalms, 25 Drawing Flgures CONTRACTION ImIm.)

PATENTED FEB 2 0 I973 3717. 445 SHEET 02 [1F 16 FIG.3

O COPPER POWDER METALLURGICAL PLATE LINER SINTERED ON THE COPPER PLATE A COPPER POWDER METALLURGICAL PLATE LINER MIXED CARBON FIBER LAMINATED LINER MOLDED FROM THE COPPER POWDER METALLURGICAL PLATE X 'LAM|NATED LINER MOLDED FROM THE COPPER POWDER METALLURGICAL PLATE MIXED CARBON FIBER 6. 1.5 I215 CONTACT PRESSURE /m INVENTORS T5 (IA/E0 yosfl m uR PATENTEBFEBZOIQ" 0; T 1 T. 445 SHEET 03 [IF 16 FIG. 40

COPPER-GRAPHITE PLATE 0 coPPER POWDER METALLURGICAL PLATE LINER AND 20.000- GRAPHITE PLATE A IR0N PowDER METALLURGICAL PLATE LINER AND IQOOO GRAPHITE PLATE :1 ALUMINUM PowDER METALLURGICAL PLATE LINER AND GRAPHITE PLATE 5.000 4.000 '5 3.000

CONTACT ELECTRIC RESISTANCE 20 l l I I l l I I I I O I 2 3 4 5 6 7 8 9 IO 'coNTAcT PREssuRE I Q/Cm I INVENTOR. Tux/v50 Y0 S/l/fiIl/IM UN/O Jl/Zl/K/ B c, osms/ saw/(4N0 MW P M PAIEIITEII E Z 3,717,445

SHEET UU'UF 16 FIG. 4b

o COPPER POWDER METALLURGICAL PLATE LINER Q LAMINATED MOLDING PLATE COMPRISING PLATEs OF 5000 THE COMPOSITIONS NOS. l, 5 AND 2 4.000- c} CoPPER PLATE 20 I I I I I l I I I I O' 2 3 4 5' 6 7 8 9 IO CONTACT PRESSURE z) INVENTORS TSUNE O YOSH/N UFIA Ku/v/o suzuk/ BY G o/// sfmmwo PIIIEIIIEII f v 3. 7 1 7, 445

' SHEET 05 0F 16 FIG. 4C

0 COPPER POWDER METALLURGICAL PLATE LINER MIXED CARBON FIBER 2O.OOO-

' A IRON POWDER METALLURGICAL PLATE LINER MIXED CARBON FIBER IO.OOO-

I3 ALUMINUM POWDER METALLURGICAL PLATE LINER MIXED CARBON FIBER 5IOOO 4OOO COPPER PLATE O 300 LL! O 5 Z O 0 2 I I I I I I l l I O I 2 3 4 5 6 7 8 9 IO CONTACT PRESSURE 2) INVENTORS 7'5 U/VEO rosy/Mum KUN/O suzu/r/ BY GOHE/ SH/KANO PATENIEDFEBZOIQ 3,717,445

sIIEET CBUF 16 FIG. 50

X COPPER-GRAPHITE PLATE 9 COPPER POWDER METALLURGICAL PLATE LINER AND 20.00% GRAPHITE PLATE A IRON POWDER METALLURGICAL PLATE LINER AND GRAPHITE PLATE IO.OOO

:1 ALUMINUM POWDER METALLURGICAL PLATE LINER ANO GRAPHITE PLATE 5.000

20 I I I L 1 Al I I I O I 2 3 4 5 6 7 '8 9 IO CONTACT PRESSURE /ch1 INVENTORS TSU/VEO YOSH/M U/PA 3M JM A/WW PAIENTED 3,717, 445

SHEET 07 OF 16 FIG. 5b

30.000 x COPPER PLATE 20.000 COPPER POWDER METALLURGICAL PLATE LINER AFTER THE THERMAL TREATMENT OF 300C.

IOOOO A LAMINATED MOLDING PLATE COMPRISING PLATES OF THE COMPOSITIONS NOS. I, 5 AND 2 AFTER THE THERMAL TREATMENT OF 300C.

CONTACT PRESSURE /m INVENTORS 7150/1/50 YOJfl/M URA KU/V/O SUZU/K/ c; OHE/ 5H/A A/VO NW al- M.

PATENIEDFEBZOW I 3,717,445

SHEET C8IIF 16 FIG. 5C

X COPPER PLATE El ALUMINUM POWDER METALLURGICAL PLATE LINER MIXED CARBON FIBER AFTER HEAT TREATMENT 20.000 OF 300C.

A IR0N PowDER METALLURGICAL LINER MIXED CARB0N FIBER AFTER HEAT TREATMENT OF 300C.

0 COPPER POWDER METALLURGICAL PLATE LINER 5000 MIXED CARBON FIBER AFTER HEAT TREATMENT 000 OF 300C.

CONTACT ELECTRIC RESISTANCE I,-

I I l I l I l I L o I 2 3 4 5 e 7 8 9 I0 CONTACT PRESSURE I z) HUN/O suzu/w BY GOHE/ mum/v0 5W, 4.14 M 41x41 CM PATENTED P81201913 3, v 1 7. 445

SHEET OSUF 16 FIG. 60

FIG. 6b

INVENTOR: TJU/VEO YOSH/NUR KUN/O SUZUKI G 0/1 5/ JH/AA VO 3M, gm 811 PATENTED P63201975 3,717. 445 SHEET 108E 16 INVENTORS TSU/VO YOSH/M URA HUN/O Sl/Zl/K/ GOHE/ SH/ffA/VO BM, JM

um r Cufl PATENTEBFEHZOIQH 3,717,445 SHEET -l2UF 16 FIG. 9a

FIG. 9b

INVENTORS SUNE O YOS/l/MURA PATENTEDFEBZOIQB 3.717. 445

SHEET 1. 3 OF 15 FIG. IOCI FIG. lOb

mnv/o 51/2 wr/ BYGOHE/ SH/KAA/O BMW- 4, #MMK CM PATENTEDFEBZBIET? 3717.445

SHEET luUF 16 FIG. HG

FiGHb INVENTORS TSU/VEO YOSH/MUHA ku/v/o suzu/r/ aoms/ S/l/k/M/O' PATENTEDFEBZOIW 3, 71 7. 445

SHEET 150F16 FIG. I20

FIG. |2b

No. I

PATENTEU FEBZUIQB T l 7. 445

SHEET 15 OF 16 FIG. I36

INVENTORS TSUNEO YO SH/MURA KUN/O $UZU/f/ BYG OHE/ S/l/KA NO A/LWMM v- M ELECTRODE HOLDER FOR ELECTRIC ARC FURNACE AND MAKE THE SAME BACKGROUND OF THE INVENTION The invention relates to an improved electrode holder liner suitable for a graphite electrode holder of the electric arc furnace, more particularly, this invention relates to the electrode holder having the porous powder metallurgical plate liner itself or those sintered on one side or both sides of a surface of the metal plate applicable to the electrode holder of the electric arc furnace.

Ordinary, it has been mainly used the electrode holder having such a structure as directly supporting the graphite electrode and supplying an electric current thereto.

However, a prior electrode holder mentioned above is easy to make a bad contact with the electrode by causing a deformation of the electrode holder itself owing to a heat hysteresis thereof during a use for long period thereby to bring a local high electric current density and said phenomena will be accelerated until the holder is damaged even if heat generated by a resistance at a contact surface of the electrode holder is effectively removed by flowing a cooling water through the electrode holder.

In such a structure of the electrode holder as mentioned above, a troublesome lying in spherical contact surface between the graphite electrode and the electrode holder results in a damage of the electrode holder until a repair becomes difficult.

In order to overcome many disadvantages as mentioned above, it has now been adopted a liner system interposed an copper plate liner between the graphite electrode and the electrode holder as shown in FIG. 1.

In the system mentioned above, although a cooling efficiency at the contact surface between the holder and the graphite electrode somewhat decreases, the bad contact between the holder and the graphite electrode may be improved thereby preventing the damage of the electrode holder. Namely the copper plate liner is able to remove at any time to polish by a grinder whereby the bad contact and a bad electric conductivity may be improved. When the copper plate liner becomes too thinner to polish, only the liner may be renewed and it makes cheaply and easily to repair.

Since in the structure of the furnace point of view the electric holder is heated by hot gas generated in the furnace and by the electric current therethrough, it is a natural matter that the copper plate liner is forced to maintain at a high temperature.

A thermal expansion coefficient of the copper plate liner differs from that of the graphite electrode as shown in Table l and the diameter of the electrode also somewhat differs from one another in the same number of an article as shown in Table 2, therefore, it is difficult to maintain a good contact in the contact surface between the holder and the graphite electrode.

TABLE l The coefficient of thermal expansion of graphite and copper The coefficient of thermal expansion X l/"C Temp. C

" JIS Japanese Industrial Standard In the recent electric arc furnace operation, it intends to operate the electric arc furnace using a high electric power as well as an ultra high electric power to improve productivity. In such situation, since larger electric current as well as higher voltage are used in the operation, the more a current density will increase in the liner location. As mentioned above, it is impossible to always maintain so as to be a good contact between the graphite electrode and the liner of the holder. Therefore, the electric current will gather into the contact location thereof whereby abnormal local heating as well as a formation of copper oxide layer may occur. Since copper oxide formed makes poor electroconductivity as well as thermal conductivity, the temperature increasement may be accelerated until the copper plate liner reaches to the damage. In order to overcome said disadvantages, the copper plate liner periodically shall be polished every few days to remove the oxide layer thereby to protect from the local heating. According to an increasement of an operating electric power, a polishing cycle of the copper plate liner will increase and a duration time for operating one cycle will decrease. Therefore a number of working times will decrease and a maintenance cost will increase as the operating electric power increase.

In higher electric power operation (so called an ultra-high power operation or U.H.P. operation informally), 2 4 times of the electric current ordinally used, result in the increasement of the electric current density whereby the trouble-some is easy to occur.

Therefore, it has been often used in U.I-I.P. operating electric arc furnace such a structure of the holder liner as supply water through the liner itself to cool thereof and as clamp more than twice times of the clamping force ordinally used.

Such the structure of the electrode holder as shown above makes it easy to form a copper oxide layer which is an electric insulating material and to spark out.

In view of said matter, it was necessary to renew the liner every week.

SUMMARY OF THE INVENTION The present invention provides a novel liner suitable for the graphite electrode holder overcoming many disadvantages and also improving the operating efficiency as well as the depression of the maintenance cost characterized in that it comprises the porous powder metallurgical plate itself, a laminated plate comprising two or more than two of the porous powder metallurgical plates having different components or those supported on a surface of the metal plate manufactured by 30 100 percent by weight of at least one of metal powder selected from the group consisting of copper, iron and aluminum powders as a main component of metal powder, 50 percent by weight of graphite powder, 0 30 percent by weight of the additional metal powder and 0 3 percent by weight of carbon fiber or graphite fiber on the weight basis of the powder metallurgical plate.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a plan elevation of the liner type electrode holder;

FIG. 2 is a side view of the electrode holder of FIG.

FIG. 3 is a characteristic curve showing a pressuredeformation of the copper powder metallurgical plate in comparison with that of the copper plate;

FIGS. 40 4c are the characteristic curves showing an interrelationship between a contact electric resistance and a contact pressure of the powder metallurgical plate of composition Nos. 2, 3 or 4; No. 7 and the laminated molding plate consisting plates of the compositions Nos. 1, 5 and 2 in order and the powder metallurgical plate of the composition Nos. l2, 13 or 14 (mixed with carbon fiber) of Table 3 respectively in comparison with those of the graphite plate measured in the room temperature;

FIGS. 5a 5c are the characteristic curves showing the interrelationship between the contact electric resistance and the contact pressure of the liner of samples shown in FIGS. 4a 4c treated by heat of 300 C. measured in an ambient temperature as well as a stationary operating condition;

FIGS. 6a 11b are diagrammatical views of the powder metallurgical plate liner of this invention;

FIGS. 6a 6b are a front view and a plan view of the liner of the powder metallurgical plate not providing any groove respectively;

FIG. 7a is a front view of the liner of the powder metallurgical plate itself providing slanting checked pattern type grooves 9 on an inner curved surface 8;

FIG. 7b is a cross sectional view along a line c c of FIG. 7a;

FIGS. 8a and 8b are a front view and a top view of the liner sintered on a side of the metal plate 10, the powder metallurgical plate 11 not providing any grooves respectively;

FIGS. 9a and 9b are a front view and top view of the liner sintered on a side of the metal plate 12, the powder metallurgical plate 13 providing vertical grooves 14 respectively;

FIGS. 10a and 10b are a front view and a top view of the liner sintered on a side of the metal plate 15, the powder metallurgical plate 16 providing horizontal grooves 17 respectively;

FIGS. 1 1a and 11b are a front view and a top view of the liner sintered on both sides of the metal plate 18 the powder metallurgical plates 19 respectively;

FIGS. 12a and 12b are a front view and a top view of the liner comprising the powder metallurgical plates laminated the powder metallurgical plates of the composition Nos. 1, 5 and 2 in order; and

FIGS. 13a and 13b are the diagrammatical views of the electrode holder suitable for the application of the liner of the powder metallurgical plate as shown in FIGS. 6a 12b burying therein.

In FIG. 1, 1 is the graphite electrode; 2, the water cooled holder; 3, the copper plate liner; 4, bus tube for supplying electric current; 5, a press machine; 6, an inlet of a cooling water; 7, an outlet thereof.

DESCRIPTION OF THE PREFERRED EMBODIMENT The porous powder metallurgical plate liner was manufactured by uniformly mixing the main component of metal powder, graphite powder, the additional metal powder and carbon fiber or graphite fiber in a predetermined amount as shown in the Table 3 and molding it to a desired form under the predetermined pressure and then sintering it at a certain temperature.

The compounding ratio of starting materials consists of 30 100 percent, preferably percent by weight of at least one of metal powder selected from the group consisting of copper, iron and aluminum powders as the main component of metal powder, 0 50 percent, preferably 3 15 percent by weight of graphite powder, 0 30 percent, preferably 2 5 percent by weight of the additional metal powder and 0 3 percent, preferably 0.2 1.5 percent by weight of carbon fiber or graphite fiber on the weight basis of the powder metallurgical plate as shown in Table 3.

It is necessary to well mix carbon fiber or graphite fiber in metal powders so as to uniformly disperse through metal powders.

Although the molding conditions may vary depending on a kind of metal powder to be compounded and a compounding ratio, it is preferable to mold compounding metal powders to a desired form under the pressure of 1.5 to 8 metric ton/cm and sinter it at the temperature of 500 to l,250 C. for 15 180 minutes.

In the manufacture of the laminated article, it is preferable to laminate layers of metal powders having the compositions No. 1, No. 5 and No. 2 as shown in Table 3 in order, and then mold said layers to the desired form and sinter it under the conditions as mentioned above.

The particle size and the purity of metal powder to be compounded are shown as Tables 4 and 5.

TABLE 4.-PURITY AN I) PARTICLE SIZE OF METAL POWDER TO BE COMPOUNDED Main component Additional metal Carbon 01' graphite Cnppvr powder Iron powder Aluminum powder Graphite powder powder fiber lnrily. Mom thnn 93.5% Orv than 1 79,. H r More than HS"? r More than 85% r Mort than 98% More than 909}. lnrtirlv. Imss than 1.000; Imss than l,t)0t) ImSS than Llltlthiun Less than 1000 Less than 2001.1 Silo Loss than Its mush Ims tlmn lb mesh. Less than 18 mesh, Less than 18 mesh", Less than 70 mesh... Chip.

I Tyler stmnlnrtl sieve.

TABLE Characteristic value of carbon or graphite fiber (monofilament) Characteristic Value Shape Specific gravity (gr/cc) 1.4-2.0 Diameter n) 7-20 Diameter (p) 720 Clip Tensile strength (kglcm 625 length Elongation 0.3-1.8 2-15 m/m The additional metal powder to be compounded belong to Fe, Cu, Sn, Al, Pb, Zn, Mg, W, Mo, Co, Ta, Cr, Ti, Be, Ag, Mn, Cd and metallic oxide thereof.

It is preferable to combine and compound iron, copper, tin, aluminum; lead, zinc, magnesium; tungsten, molybdenum; cobalt, tantalum, chrom; titanium, beryllium; silver, manganese, cadmium as the additional metal powder.

It is preferable to select a round particle size of metal powder, a uniform particle form, a minimum pressure of molding press and such a sintering temperature as occurs a surface diffusion on metal powders in order to manufacture the porous powder metallurgical plate liner of this invention.

In view of that the contact surface between the liner and the holder is a curved one, if a curvature between the liner and the holder is different from each other by a minute, the copper plate liner will contact with the holder in some points or lines form thereby increasing the contact resistance of the electric current.

In case that the powder metallurgical plate liner is used instead of the copper plate liner as shown in FIG. 3, the contact electric resistance thereof is small in comparison with that of the copper plate liner while operating in spite of the porous structure thereof since the plate liner bears a large compressive deformation thereby maintaining a good contact by a clamping pressure of ordinary 5 30 kg/cm in comparison with the copper plate owing to the porous structure of the liner.

FIG. 3 shows a characteristic feature of a compressive deformation of the copper powder metallurgical plate liner in comparison with that of the copper plate, taking a clamping pressure (kg/cm) in ordinate, and the compressive deformation of the copper powder metallurgical plate liner sintered on the copper plate in abscissa, in the curve plotted by the sign@; those of the copper powder metallurgical plate liner mixed carbon fiber therein, in the curve plotted by the sign A; those of the laminated liner molded from the copper powder metallurgical plates, in the curve plotted by the sign@;

those of the laminated liner (a dimension of sample of 40 mm X 20 mm X mm) molded from the copper powder metallurgical plates mixed carbon fiber therein in the curve plotted the sign X.

FIGS. 4a 40 show measuring results relative to the interrelationship between the contact electric resistance and the clamping pressure of the powder metallurgical plate liners of this invention in the room temperature using the size of 80 mm X 10 mm taking the clamping pressure (kglcm in abscissa and the contact electric resistance (#9) in ordinate in comparison with that of the copper plate shown in the curve plotted by the sign X.

FIG. 4a shows a characteristic feature of the interrelationship between the contact electric resistance and the clamping pressure of the copper powder metallurgical plate liner having the composition No. 2 in the curve plotted by the sign(); that of the aluminium powder metallurgical plate liner having the composition No. 3 in the curve plotted by the signlIl; that of the iron powder metallurgical plate liner having the composition No. 4 in the curve plotted by the sign A.

FIG. 4b shows a characteristic feature of the interrelationship between the contact electric resistance and the clamping pressure of the copper powder metallurgical plate liner having the composition No. 7 in the curve plotted by the sign that of the laminated molding plate (the combination of the plates having the composition Nos. 1, 5 and 2 in order) in the curve plotted by the sign A.

FIG. 4c shows a characteristic feature of the interrelationship between the contact electric resistance and the clamping pressure of the copper powder metallurgical plate liner mixed therein carbon fiber of the composition No. 12 in the curve plotted by the sign@; that of the ironpowder metallurgical plate liner mixed therein carbon fiber of the composition No. 13 in the curve plotted by the sign A; and that of the aluminum powder metallurgical plate liner mixed therein carbon fiber of the composition No. 14 in the curve plotted by this signl].

The said experimental conditions correspond to those before the circular operation. In this case, it has found that the metal powder metallurgical plate liner except the copper powder metallurgical plate liner possess larger contact electric resistance than that of the copper plate owing to the inherent electric conductivity of metal.

FIGS. 5a 56 show the contact electric resistance of the samples shown in FIGS. 4a 40 after the thermal treatment of 300 C. at the normal room temperature in comparison with the contact electric resistance of the corresponding samples untreated.

It has been found from the results obtained by FIGS. 50 that the contact electric resistance between the copper powder metallurgical plate liner and the graphite plate in a range of the clamping pressure of 5 30 kg/cm is smaller than that of the copper plate liner in view of that the contact resistance between the copper plate liner and the graphite electrode is greatly effected with the formation of the oxide layer while that of the powder metallurgical plate liner is less effected with the formation of the oxide layer.

In the copper plate liner, it was necessary to minutely finish the surface of the copper plate liner, while in the powder metallurgical plate liner of this invention, the increasement of the contact resistance resulting from the bad contact between the liner and the graphite electrode may not occur even if not efi'ecting any surface finishing of the liner since the pressure deformation of the holder is possible by means of the clamping pressure.

In the powder metallurgical plate liner, although the liner having the flat curved surface has been explained for convenience sake, a flat plate liner having vertical grooves, horizontal grooves or lattice-like grooves, can be used in a form of that sintered on one side or both sides of the metal base plate, or the laminated form. And also, if necessary, said powder metallurgical plate liner mixed with carbon fiber or graphite fiber can be used in the same way. 

1. An electrode holder for a graphite electrode of an electric arc furnace, said electrode holder having a liner having a surface that is adapted to engage and conform to the surface of the electrode and said liner comprising a poRous, sintered, powder metallurgical member comprising from 30 to 100 percent by weight of metal powder selected from the group consisting of copper, iron and aluminum powders and mixtures thereof, from 0 to 50 percent by weight of graphite powder, from 0 to 30 percent by weight of an additional metal powder selected from the group consisting of tin, lead, zinc, magnesium, tungsten, molybdenum, cobalt, tantalum, chromium, titanium, beryllium, silver, manganese and cadmium powders and mixtures thereof, and from 0 to 3 percent by weight of at least one of the group consisting of carbon fiber and graphite fiber and mixtures thereof.
 2. An electrode holder for a graphite electrode of an electric arc furnace, said electrode holder having a liner having a surface that is adapted to engage and conform to the surface of the electrode and said liner comprising a porous, sintered, powder metallurgical member comprising from 80 to 95 percent by weight of metal powder selected from the group consisting of copper, iron and aluminum powders and mixtures thereof, from 3 to 15 percent by weight of graphite powder, from 2 to 5 percent by weight of an additional metal powder selected from the group consisting of tin, lead, zinc, magnesium, tungsten, molybdenum, cobalt, tantalum, chromium, titanium, beryllium, silver, manganese and cadmium and mixtures thereof and from 0.2 to 1.5 percent by weight of a material selected from the group consisting of carbon fiber and graphite fiber and mixtures thereof.
 3. An electrode holder according to claim 1 having a solid metal plate as a base and a porous, powder metallurgical liner sintered on one side thereof.
 4. An electrode holder according to claim 1 having a solid metal plate as a base with a porous outer metallurgical liner sintered on both sides thereof.
 5. An electrode holder according to claim 1 wherein the liner comprises two or more porous, powder metallurgical members laminated together. 